Water, wastewater, and industrial filtration units typically have an underdrain system for supporting filter media and spacing the filter media apart from the bottom of the filter. The underdrain system provides support for the filter media, collects the filtered water that passes through the media and uniformly distributes backwash water, backwash air, or a combination of both, across the filter.
Formations of support blocks are often used to construct the underdrain system. The support blocks may be made of pre-cast concrete blocks or concrete filled plastic jacketed blocks. The high-strength concrete blocks are placed side-by-side and end-to-end in the bottom of the filter to form a “false bottom.” The blocks provide support for the filter media and are shaped to collect the filtered water that passes through the media.
In operation, a media filter will periodically require cleaning by backwashing the filter. In addition to shaping for collection, the blocks have conduits, commonly known as laterals, to allow for the passage of air or water used as a backwash. Problems can occur during backwash because the upward pressure of the air and/or water against the blocks is too forceful. Sometimes the pressure can fall within a range of 2 psi to 6 psi. Such strong pressure tends to dislocate the blocks, a process known as uplift. When uplift occurs, filter media drops onto the pipes and damages the infrastructure. Repairing such damage is costly. In addition, the costs of emptying the filter and realigning the blocks are also expensive. The process is labor intensive and requires substantial downtime of the filter. As a consequence, there is a need for a support system that resists uplift as well as side movements.
Existing systems for filter media support rely on the weight of the blocks to prevent block movement, use grout to fill the gaps between the blocks or use side rails to align the blocks side-to-side in the filter basin. Other systems use a series of modular, interconnected air duct blocks such that the interiors of separate air duct blocks are in fluid communication with one another to supply backwash gas through a single source of gas supply. These underdrain block designs offer only a limited amount of backwash stability and some are difficult to assemble. Because stability in the support system is important to avoid damage to the infrastructure, there is a need for an improved underdrain system that is easily assembled and will limit the movement of the underdrain blocks during backwash procedures in both the vertical and horizontal directions.
Definitions
For the purposes of this invention, a guide is defined as a device for steadying or directing the motion of a slide.
For the purposes of this invention, a slide is defined as an extension that is steered by one or more parts within which it slides.
For the purpose of this invention, a nub is defined as a protuberance projecting from a surface.